ffmpeg/libavcodec/rangecoder.h

   1 /*
   2  * Range coder
   3  * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
   4  *
   5  * This file is part of FFmpeg.
   6  *
   7  * FFmpeg is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  *
  12  * FFmpeg is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with FFmpeg; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 /**
  23  * @file
  24  * Range coder.
  25  */
  26
  27 #ifndef AVCODEC_RANGECODER_H
  28 #define AVCODEC_RANGECODER_H
  29
  30 #include <stdint.h>
  31
  32 #include "libavutil/common.h"
  33 #include "libavutil/avassert.h"
  34
  35 typedef struct RangeCoder {
  36     int low;
  37     int range;
  38     int outstanding_count;
  39     int outstanding_byte;
  40     uint8_t zero_state[256];
  41     uint8_t one_state[256];
  42     uint8_t *bytestream_start;
  43     uint8_t *bytestream;
  44     uint8_t *bytestream_end;
  45 } RangeCoder;
  46
  47 void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size);
  48 void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size);
  49 int ff_rac_terminate(RangeCoder *c);
  50 void ff_build_rac_states(RangeCoder *c, int factor, int max_p);
  51
  52 static inline void renorm_encoder(RangeCoder *c)
  53 {
  54     // FIXME: optimize
  55     while (c->range < 0x100) {
  56         if (c->outstanding_byte < 0) {
  57             c->outstanding_byte = c->low >> 8;
  58         } else if (c->low <= 0xFF00) {
  59             *c->bytestream++ = c->outstanding_byte;
  60             for (; c->outstanding_count; c->outstanding_count--)
  61                 *c->bytestream++ = 0xFF;
  62             c->outstanding_byte = c->low >> 8;
  63         } else if (c->low >= 0x10000) {
  64             *c->bytestream++ = c->outstanding_byte + 1;
  65             for (; c->outstanding_count; c->outstanding_count--)
  66                 *c->bytestream++ = 0x00;
  67             c->outstanding_byte = (c->low >> 8) & 0xFF;
  68         } else {
  69             c->outstanding_count++;
  70         }
  71
  72         c->low     = (c->low & 0xFF) << 8;
  73         c->range <<= 8;
  74     }
  75 }
  76
  77 static inline int get_rac_count(RangeCoder *c)
  78 {
  79     int x = c->bytestream - c->bytestream_start + c->outstanding_count;
  80     if (c->outstanding_byte >= 0)
  81         x++;
  82     return 8 * x - av_log2(c->range);
  83 }
  84
  85 static inline void put_rac(RangeCoder *c, uint8_t *const state, int bit)
  86 {
  87     int range1 = (c->range * (*state)) >> 8;
  88
  89     av_assert2(*state);
  90     av_assert2(range1 < c->range);
  91     av_assert2(range1 > 0);
  92     if (!bit) {
  93         c->range -= range1;
  94         *state    = c->zero_state[*state];
  95     } else {
  96         c->low  += c->range - range1;
  97         c->range = range1;
  98         *state   = c->one_state[*state];
  99     }
 100
 101     renorm_encoder(c);
 102 }
 103
 104 static inline void refill(RangeCoder *c)
 105 {
 106     if (c->range < 0x100) {
 107         c->range <<= 8;
 108         c->low   <<= 8;
 109         if (c->bytestream < c->bytestream_end)
 110             c->low += c->bytestream[0];
 111         c->bytestream++;
 112     }
 113 }
 114
 115 static inline int get_rac(RangeCoder *c, uint8_t *const state)
 116 {
 117     int range1 = (c->range * (*state)) >> 8;
 118
 119     c->range -= range1;
 120 #if 1
 121     if (c->low < c->range) {
 122         *state = c->zero_state[*state];
 123         refill(c);
 124         return 0;
 125     } else {
 126         c->low  -= c->range;
 127         *state   = c->one_state[*state];
 128         c->range = range1;
 129         refill(c);
 130         return 1;
 131     }
 132 #else
 133     {
 134         int one_mask one_mask = (c->range - c->low - 1) >> 31;
 135
 136         c->low   -=           c->range  & one_mask;
 137         c->range += (range1 - c->range) & one_mask;
 138
 139         *state = c->zero_state[(*state) + (256 & one_mask)];
 140     }
 141     refill(c);
 142
 143     return one_mask & 1;
 144 #endif
 145 }
 146
 147 #endif /* AVCODEC_RANGECODER_H */